It cited the head of Manbij's health committee as saying that 18 people had been killed, including the US soldiers, and that another 18 had been wounded.

Image copyrightAFPImage caption
US troops used armoured vehicles to patrol the centre of Manbij following the attack

US Central Command later confirmed that four Americans were killed.

"Two US service members, one department of defence (DoD) civilian and one contractor supporting DoD were killed and three service members were injured while conducting a local engagement in Manbij," it said in a statement.

Last month, President Donald Trump announced that the US would begin pulling out all its 2,000 troops from Syria because IS had been "defeated".

Opponents of the withdrawal stressed that although IS now controlled only 1% of the territory they overran five years ago, the group had not disappeared entirely.

Republican Senator Lindsey Graham, who has previously criticised Mr Trump's decision to withdraw troops from Syria, said on Wednesday that the move could encourage IS attacks and "set in motion enthusiasm by the enemy we're fighting".

"We have crushed the [IS] caliphate and devastated its capabilities. As we begin to bring our troops home... we will never allow the remnants of [IS] to re-establish their evil and murderous caliphate."

A recent US report said there were still as many as 14,000 IS militants in Syria and even more in neighbouring Iraq - and that they were expected to shift to guerrilla tactics in an attempt to rebuild their network.

Syrian Kurds also fear that Manbij and other towns they control near the border with Turkey might come under attack by the Turkish military, which wants to clear them of the Kurdish People's Protection Units (YPG) militia.

The Turkish government considers the YPG an extension of the banned Kurdistan Workers' Party (PKK), which has fought for Kurdish autonomy in Turkey for three decades. However, it denies any direct organisational links to the group.